Files
nearle_pos/pubspec.yaml
Suriya 0a49323858 Drain bills to the back office automatically, over MQTT or HTTP
Turns the orders table into a queue that empties itself. Bills were only
uploaded when a cashier pressed Sync at end of day; a till that was never
pressed held a day's takings indefinitely.

Drain engine (lib/data/sync/sync_engine.dart)
- Triggers on sale committed, network regained, 5-minute poll, head-office
  request, and the manual button.
- Single flight: a busy till firing a trigger per sale would otherwise have
  several passes reading the same pending rows and send every bill twice.
  A trigger arriving mid-drain is queued and replayed, so nothing is dropped.
- Exponential backoff with +/-20% jitter to a 5-minute ceiling. The jitter
  matters: a store's terminals all fail at the same instant when the line
  drops, and would retry in lockstep without it.
- Halts rather than loops on a failure retrying cannot fix (bad credential,
  refused batch). Pressing Sync clears the halt.

Transports (lib/data/remote/)
- OrderTransport interface; MQTT, HTTP and simulated implementations. The
  repository does not know which is in use.
- MQTT: QoS 1 uplink, application-level ACK correlated by batch_id on a return
  topic, retained Last Will for terminal-offline detection, downlink for
  catalogue pushes and remote sync requests.
- A broker PUBACK is never treated as acceptance. It means the broker holds
  the bytes, not that the ledger took the sale. Only ids the back office names
  are marked synced; silence leaves a bill pending.
- HTTP carries a stable idempotency key across retries of the same bills.

Retention
- Accepted bills are kept 7 days instead of deleted, so a batch the back
  office later loses can be re-sent in full. Purged after that; archived
  totals stay forever.
- forBusinessDate now reads pending rows only. A retained bill exists in both
  the orders table and day_archive, and summing both would overstate the day.

Fixes found while building this
- SyncEngine._refreshPending wrote state.copyWith(pending: await ...). Dart
  evaluates the receiver before the awaited argument, so a connectivity drop
  during the wait was silently overwritten by the stale snapshot. Caught by
  the first run of the new engine tests.
- PrinterSettingsController wrote state after four awaits with no mounted
  check, throwing "used after dispose" when Settings was left mid-load. This
  was pre-existing and reached the cashier as a red screen.

Also
- Header pill now reports real sync state: LIVE / n QUEUED / SYNCING /
  SYNC HALTED, with an explanation of where the bills are.
- Settings shows the route, last upload, next retry and retention window.
- docs/sync-contract.md states what the back office must implement, including
  the idempotency requirement that at-least-once delivery makes mandatory.

Tests: 90 -> 129 passing. New coverage for backoff shape and jitter band,
single flight, halting, ACK correlation and partial acceptance, at-least-once
duplicate handling, retention and purge, and no double-counting after a sync.
Suite run six times clean.

Not addressed: bills already synced by an older build went up overstated and
still need server-side reconciliation. Broker credentials have no Settings
editor yet.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-08-01 10:57:29 +05:30

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YAML

name: nearle_pos
description: Nearle POS — enterprise Point of Sale for supermarkets, grocery, pharmacy and retail.
publish_to: "none"
version: 1.0.0+1
environment:
sdk: ">=3.6.0 <4.0.0"
dependencies:
flutter:
sdk: flutter
# State management
flutter_riverpod: ^2.5.1
# Routing
go_router: ^14.2.0
# Value equality for domain entities
equatable: ^2.0.5
# Formatting & ids
intl: ^0.19.0
uuid: ^4.4.0
# UI
google_fonts: ^6.2.1
flutter_animate: ^4.5.0
# Local persistence — SQLite is the source of truth on the terminal
sqflite: ^2.3.3
sqflite_common_ffi: ^2.3.3
path: ^1.9.0
# Sharing the bill to WhatsApp
url_launcher: ^6.3.0
# Peripherals: scanner beeps and thermal receipt printing
audioplayers: ^6.0.0
pdf: ^3.11.0
printing: ^5.13.0
mqtt_client: ^10.11.11
connectivity_plus: ^7.3.1
http: ^1.6.0
dev_dependencies:
flutter_test:
sdk: flutter
flutter_lints: ^4.0.0
flutter:
uses-material-design: true
assets:
- assets/sounds/